Parent U.S. patent application Ser. No. 630,938 describes two proteins that were isolated from bovine bone. These proteins exhibited in vitro chondrogenic activity. Further characterization and testing of these two proteins revealed that one of them may be the same polypeptide as a human placenta-derived polypeptide called "beta type transforming growth factor" (TGF-.beta.) and described in International patent application PCT/US83/01460 published 29 Mar. 1984 under No. WO 84/01106 and EPA 84450016.5 published 19 Dec. 1984 under No. 0128849. The other has a different partial amino acid sequence than that reported for the human placenta-derived TGF-.beta., but is active in the same anchorage-independent cell growth assay as was used to characterize the biological activity of TGF-.beta..
There have been prior attempts to identify and isolate factors in bone that are involved in stimulating bone growth. U.S. Pat. No. 4,294,753 to Urist reports the preparation of a crude "bone morphogenic protein" by extracting demineralized bone with urea or guanidine hydrochloride and reprecipitating protein from the extract. Urist subsequently reported (Urist, M. R., Clin Orthop Rel Res (1982) 162: 219) that ion exchange purification of this crude protein mixture yielded an activity that was unadsorbed to carboxymethylcellulose (CMC) at pH 4.8. Urist's most recent reports (Science (1983) 220: 680-685 and Proc Natl Acad Science (USA) (1984) 81: 371-375) described BMPs having molecular weights of 17,500 and 18,500 daltons.
U.S. Pat. No. 4,434,094 reports the partial purification of a bone generation-stimulating, bone-derived protein factor by extraction with chaotropic agents, fractionation on anion and cation exchange columns, and recovery of the activity from a fraction adsorbed to CMC at pH 4.8. This new protein fraction was termed "osteogenic factor" (OF) and was characterized as having a molecular weight below about 30,000 daltons and as tracking the purification process described. The proteins of the current invention were purified to homogeneity using a purification procedure that is similar in part to that disclosed in U.S. Pat. No. 4,434,094.